EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.4.5 Oxidation & Reduction

EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.4.5 Oxidation & Reduction

Oxidation & Reduction


Oxidation & reduction in terms of oxygen

  • The reactions of metals with oxygen, such as in iron rusting can be classified as oxidation
  • Oxidation is any reaction in which a substance gains oxygen
  • The opposite of oxidation is reduction
  • Reduction is a reaction in which a substance loses oxygen
  • For example, the displacement reaction between zinc and copper(II)oxide can be classified as a redox reaction


Zn    +     CuO    →    ZnO    +    Cu


zinc + copper(II) oxide → zinc oxide + copper


  • Oxidation cannot occur without reduction happening simultaneously, hence these are called redox reactions
  • The copper(II)oxide supplies the oxygen, so it is the oxidising agent
  • The zinc is the reducing agent because it removes the oxygen




Oxidation & Reduction in terms of electrons

  • Displacement reactions can be analysed in terms redox reactions by studying the transfer of electrons
  • For the example of magnesium and copper sulfate, a balanced equation can be written in terms of the ions involved:


Mg (s) + Cu2+ (aq) + SO42- (aq) → Mg2+ (aq) + SO42- (aq) + Cu (s)


  • The sulfate ions, SO42-, appear on both sides of the equation unchanged hence they are spectator ions and do not participate in the chemistry of the reaction so can be omitted:


Mg (s) + Cu2+ (aq)  → Mg2+ (aq)  + Cu (s)

  • This equation is an example of a balanced ionic equation which can be further split into two half equations illustrating oxidation and reduction individually:


Mg → Mg2+ + 2e


Cu2+ + 2e→ Cu

  • The magnesium atoms are thus oxidised as they lose electrons
  • The copper ions are thus reduced as they gain electrons
  • These equations illustrate the broader definition of oxidation and reduction in terms of electron transfer:
    • Oxidation is the loss of electrons
    • Reduction is the gain of electrons






'OIL RIG' is a useful mnemonic to help remember the definitions of oxidation and reduction